Electrical method for conversion of molecular weights of particulates

ABSTRACT

An electrical apparatus is provided for the conversion of compounds, elements, or mixtures which are in particulate form, into new compounds, elements or mixtures in gaseous, liquid, or particulate form. In a reaction chamber, particulates are mechanically transported into a first region of high electric field, where they acquire a charge and are projected into a second region in which a low-density plasma is maintained. Energetic plasma ions strike the surfaces of the particulates, causing chemical reactions and release of both neutral and ionic products species. Charge exchange on particulates causes the reduced-size particles to fall back into the first region, where the charging recurs and the cycle is repeated. Gaseous and particulate products are removed from the chamber. In one application, naturally-occurring ores may be reduced by a methane plasma; in another, coal may be converted in a methane plasma to intermediate range hydrocarbons.

This is a division of application Ser. No. 08/049,867, filed Apr. 20,1993, now U.S. Pat. No. 5,356,524.

The present invention generally relates to the conversion of themolecular weight of compounds, elements or mixtures thereof, availablein particulate form, into gases, liquids, and particulates containingdifferent compounds, elements, and mixtures thereof, which are morevaluable for industrial, commercial and consumer use. The invention moreparticularly may be applied to the reduction of metallic ores inparticulate form, by an energetic low-density hydrogen-and methyl-ionplasma, which attacks the surfaces of the particles to remove oxygen,sulfur, and other elements and produces a wide variety of gaseous,liquid, and particulate output compounds which can be separated usingknown temperature/pressure distillation techniques. The invention mayadditionally be more particularly applied to the hydrogenation, andgasification, of coal particulates by an energetic low-densityhydrogen-and methyl-ion plasma, which produces a wide variety of usefulhydrocarbon gases and liquids.

BACKGROUND OF THE INVENTION

Metal-bearing ores occur often in nature as oxides, such as iron oxide,chromium oxide, vanadium oxide, titanium oxide, aluminum oxide, andsilicon dioxide. The most obvious attempts to directly reduce these oresby contacting them with hydrogen have been impractical due to the costof pure industrial hydrogen, and the high temperatures involved for thereaction. Processes of this type are typically conducted in chambersisolated from the oxygen of the air. One approach has been to usesynthesis gas, a mixture of H₂ and CO obtained by reacting steam andcarbon (or a hydrocarbon) at high temperature. Reaction of the hydrogenwith the oxygen in the ore produces water, and the reaction of thecarbon monoxide with the oxygen in the ore produces carbon dioxide.Another approach has been to use methane as a reducing gas temperaturesin the order of 950° C. to 1200° C., as taught in U.S. Pat. No.4,268,303. Using this approach on iron ore, moving-bed reactors andexpensive heaters are needed, methane pyrolysis and carbon depositiontakes place, and sintering of the iron particles into agglomerates is aproblem. The operation of a moving-bed reactor with three zones isdescribed in U.S. Pat. No. 4,556,417, which operates at only 900° C. to960° C. with natural gas, and which avoids agglomerates. Considerableheat input is still necessary.

The use of an argon inert-gas plasma torch, projecting a stream ofhigh-temperature argon ion onto the top surface of a crucible containingore particulates, and with the injection of neutral methane gas onto theheated surface by means of a separate water-cooled lance, was describedby Vogel et al. (Steel Research, 60, pp. 177-181 (1989)). This reliesupon argon ion energy transfer to the neutral methane above theparticulates, argon ion and argon neutral energy transfer to the exposedtop layer of the particulates in the crucible, and the thermodynamics ofthe reduction reactions at high temperatures. The kinetics of oxygenremoval are constrained by the mixing of unreduced particulates andreduced metal. It was not possible to reduce pure titanium oxide. Sincethis process took place at nearly atmospheric pressure, there wasconsiderable energy loss from the argon arc, via the ambient gasneutrals, to the walls of the chamber as well as to the crucible. Theuse of a plasma torch to effect high temperatures, 6000° K. to 10,000°K., which can be used to melt refractory metals, to transfer energy tothe surfaces of particulates, and to cause particulates to fuse to oneanother or to adjacent cold surfaces is well known. Such plasma torchesare generally operated with a pure feed gas, such as argon, although theuse of hydrogen can be envisioned provided that the ionic attack ofplasma torch electrodes can somehow be avoided. The use ofhydrocarbon-containing gases in a plasma torch is employed for theproduction of acetylene and/or carbon black, as the plasma energeticscause cracking of the gaseous hydrocarbon feedstock. A method isdescribed in U.S. Pat. No. 5,105,028 for using a plasma torch and afeedstock gas mixture including a hydrocarbon-containing gas and aheteroatom containing gas, ionizing the mixture, and creating a morecomplex compound such as an alcohol or phenol, by ion interaction in theplasma. The electric arc is also described in U.S. Pat. No. 4,566,961 asproviding the energy for a process of combination of high molecularweight carbonaceous material with the hot gases containing C₁ -C₄saturated hydrocarbons from the arc, so as to produce low molecularweight hydrocarbon products. This process is operated at high,near-atmopsheric pressures, and requires considerable input power due tothe energy transfer by ambient neutrals to the walls of the enclosure.Moreover, the probability of repetitive interaction of the particulates(if coal is the type of high-molecular-weight carbonaceous feedstockused) with the available C₁ -C₄ hot gases, is limited.

The use of a low-density plasma containing hydrocarbon ions and methylions, inside of an array of tubular elements, is described in U.S. Pat.No. 5,019,355, as a method for the production of higher hydrocarbons byion-impact-stimulated chemical reactions at the interior surfaces of thetubular elements. Another U.S. Pat. No. 5,414,715 describes the use of aplasma and a set of electrode arrays to accomplish conversion ofcompound gases into other compound gases. However, the use ofparticulates in such apparatus is problematic, as the particulates wouldaccumulate and clog the apertures or tubular elements described,impairing their function.

OBJECTS OF THE INVENTION

It is the object of this invention to convert the molecules in a streamof particulates into different molecules which may be output in gaseous,liquid or solid particulate form, by causing the repetitive interactionof the particulates with the ions and electrons of a suitablelow-density plasma. It is a more particular objective of this inventionto enable the reduction of metallic ores to elemental metals using alow-density methane plasma. It is a further particular objective of thisinvention to enable the conversion of coal particulates intointermediate-range hydrocarbon gases and liquids using a low-densitymethane plasma.

SUMMARY OF THE INVENTION

A stream of particulates is first put into contact with a metallicelectrode of negative polarity, in a region of electric field producedby a second, adjacent, positive electrode. The particulates acquireelectrons by conduction from the negative electrode, and are thenprojected, under the combined forces of gravity and the electric field,into a second region which is free of strong d.c. electric field butwhich contains a time-varying electric field of sufficient magnitude tocause ionization of feedstock gas neutrals which are injected into thesecond region at a pressure well below atmospheric pressure. Thenegatively-charged particulates are impacted by the positively-chargedenergetic ions; the surface interactions thus induced on theparticulates lead to destruction of the chemical bonds of the solid, andthe emission from the particulate surface of new compounds, most ofwhich are gaseous neutrals, and some of which are ions. Reduction of thesize of the particle, and chemical removal of oxygen, sulfur, andsimilar elements from the particle in the case where a hydrogen-ion andmethyl-ion plasma is used, is the result. After charge neutralization ofa particle due to multiple ion impacts, the gravity force dominates andreturns the particle, now smaller, back to the first region where itcontacts the negative-polarity electrode again. It recharges withelectrons, and the process repeats, further diminishing the particlesize. If the gas which is used to produce the low-density plasma ischosen properly, it is possible that all of the new compounds generatedby the process will be gaseous, and can be pumped away and separated bylow temperature/low pressure distillation techniques. In the case ofother gases, metallic or compound particles may remain and may betransferred laterally along the negative electrode, by vibration orother means, to a region free of electric field, for removal from theapparatus. Fine particulates of natural ores may be reduced in this way.If high-carbon-number carbonaceous particles such as oil shale, tarsands or coal are used, the combination of them with ions in a hydrogenor methane low-density plasma will produce intermediate weighthydrocarbon gases, along with other products. In every case in which ahydrocarbon source is used for the plasma, a spectrum of new hydrocarbongases is created, along with hydrogen and other gases.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1: A diagram of the apparatus example for conversion of molecularweights of particulates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and in particular to FIG. 1, there isshown an electrical apparatus 10 for the conversion of molecular weightsof particulates, comprising a chamber 12 with walls constructed ofmetal, glass, ceramic, or other material providing for a hermetic seal,with an inlet gas source 27, an outlet gas port 28, an inlet port forparticulates 29, transmitting particles through an air lock 30, in whichadmitted air is evacuated through a pumping port 31 before the particlesare allowed to enter the main feed section 32. A particulate output portis provided with a similar airlock 34 which also has a pumping port 35to evacuate air before a new charge of output particles are allowed toenter the airlock. Electrical insulators 37 are provided, isolating theplasma excitation electrode 38 from the grid electrode 39 and from thenegative electrode 40. The surface of the negative electrode 40 ismechanically activated to convey particles either steadily or byvibration, with a mechanical activator 41 connected to electrode 40.Output particulates are discharged through output port 33 and arecollected externally in a container 42. A high-voltage external d.c.voltage source 43 is connected between negative electrode 40 and porous,mesh or grid-type electrode 39. A second external d.c. voltage source 44is connected in series with an external a.c. voltage source 45, andtheir output is connected between grid electrode 39 and plasmaexcitation electrode 38. A low-level source of electrons 46 is connectedto the negative electrode.

Briefly describing the operation of the device in the mode in whichmetallic ores are reduced, the input gas such as methane CH₄ is admittedthrough input source port 27, which particulates in the size rangepreferably less than two micrometers in maximum diameter are admittedthrough particulate port 29, airlock 30, and are allowed to flow underthe forces of gravity down the main feed section 32 and onto thecombined conveyor system and negative electrode 40 which is mechanicallyactivated by activator 41. Particles move into a region of high-electricfield caused by the presence of the voltage on grid electrode 39 causedby the external voltage source 43. Each particle may be regarded from anelectrical circuit equivalent viewpoint as a series connection of acapacitance, related to particle size, shape, and dielectric constant,and a resistance, related to particle size, shape, surface resistivity,and volume resistivity. In the region of high electric field, there is apotential difference imposed across the particle, and an electroncurrent flows from the negative electrode into the particle, followingan exponential function of time and resulting in the accumulation of anet negative charge on the top surface of the particle. The electricfield intensity must be large enough so that the total charge q thusaccumulated, multiplied by the electric field strength E, results in anupward electrical force qE on the particle which slightly exceeds thedownward gravity force, mg, after some elapsed time t which typicallywould be equal to or less than the time constant T for theaforementioned exponentially-varying charging process. Due to the netupward force, the particle is separated from the negative electrode 40and is projected upward through the grid electrode 39, passing into theplasma-active region bounded by grid electrode 39 and plasma excitationelectrode 38. A minor fraction of the particles may strike the gridelectrode elements, release some of their negative charge, and fall backdown to negative electrode 40 where the charging process is repeated andthey are again projected upwards. The negatively-charged particlespassing through the grid electrode 39 enter a region in which acomparatively weak d.c. electric field exists, produced by the externald.c. voltage source 44, together with a superimposed strongeralternating-polarity electric field produced by the external a.c.voltage source 45. Methane gas is injected into the same region, andionization of methane neutral molecules is caused by electrons from thesuitable electron source 46, which may be field emission, or photoemission, or thermionic, or beta-emitting radioactive source. Theelectrons, the hydrogen ions and the methyl ions thus created areaccelerated to high-kinetic energy, in the range 10 eV to 60 eV or more,by the strong a.c. electric field and the superimposed d.c. electricfield. However, the frequency of the a.c. voltage source 45 is chosen tobe high enough that only the electrons and the ions in the region movean appreciable distance and acquire energy during each half period ofthe a.c. voltage source 45. In contrast, because of the much greatermass of the particles, the particles are unable to move a significantdistance during the half period of the a.c. voltage source 45, and donot therefore absorb much energy from source 45. The alternatingreversal of direction of the a.c. electric field results in only a smalleffect upon the trajectories of the particles, whereas the electrons andthe ions gain 10 eV to 60 eV of kinetic energy during each half cycle ofthe a.c. source 45. Collisions take place, especially of the type inwhich the positive hydrogen and methyl ions strike the surfaces of thenegatively-charged particles. The energetics of ion impact causechemical reactions on the surfaces, in which the natural chemical bondsin the particulate material are broken, and new bonds are formed betweenthe impacting ions and the available source atoms on the particles. Forexample, on a particle composed of a metallic oxide, the oxygen maycombine with the impacting hydrogen to form a hydroxyl, and a secondhydrogen ion impact may cause formation of a neutral water molecule.This would be desorbed readily from the surface in future impacts andwould eventually appear in the gaseous output. Another competing processwould be impaction of methyl ions, forming possibly water, and possiblycarbon monoxide or carbon dioxide. A mixed layer of carbon, hydrogen,oxygen, and the metallic element would be formed on the surface, withstable gaseous neutral molecules leaving the layer, in significantquantities, immediately after an ion impact. Additional stable gasspecies may include metallic hydrides, organometallic gases such asthose of dimethyl, trimethyl, or tetramethyl type, and perhaps alcoholsand more complex organometallic compounds. It is also inevitable thathigher hydrocarbon species will be created on, and released from, thesurface, including acetylene, ethylene, ethane, propane, propene,propyne, and larger species. All such gases may be expected to appear inthe gaseous output 28. Both unreacted methane and surface-producedmethane will also appear in the output 28 as will hydrogen. Positive ionbombardment of the negatively-charged particulates will cause a changein net charge of the particulates, and if some particles actually strikethe electrode 38 they will transfer electrons to the electrode and losecharge. For some particles, an elastic bounce of a particle from thesurface of electrode 38, and the downward force of gravity, will movethose particles back down through grid electrode 39 and to negativeelectrode 40. Other particles will have their negative chargeneutralized by positive ion impact and will also move down through gridto electrode 40. The particle mass will be smaller due to the many ionicimpact events and the mass of gases lost from the surface of theparticle. The process described above will then repeat, for the smallerparticle, until the particle disappears, or until a stable small finalparticulate (such as a pure metal) is formed. Final particles areconveyed to the output airlock 34 and emerge in the container 42.Additional interactions include particle-particle collisions, whichcause rotation of particles and the acquisition of transverse momentum.This tends to expose of all sides of each particle to energetic ionbombardment. Grazing collision angles between ions and particle surfacesare very common, and escape of the resulting neutral gas moleculeproducts from the surface is thereby favored. Some energy of ionicimpact will be transformed, over times of the order of nanoseconds tomicroseconds, into heating--e.g. random thermal motion--of the atomsinside of the particle. This will help to cause the release of neutralgas species from particle surfaces, and will promote reactions at thesurfaces. The recharging of the particles, when they are in contact withnegative electrode 40 for the second and subsequent times, is enhancedby both the bombardment-induced conductivity of the particle surface,and by the presence of discontinuous islands of reduced metal at thesurface which have a semiconducting character. The formation of acomplex carbon-hydrogen-oxygen-metallic amorphous layer, with voids, atthe particle surface, forestalls any tendency towards agglomeration ofparticles.

Bombardment of grid electrode 39 by positive ions will cause chemicalreactions among the various neutral species adsorbed on the gridsurfaces, and with the impacting ions. This can be controlled byadjustment of the polarity and magnitude of external d.c. supply voltagesource 43, so that positive ions with energies of 10 eV to 60 eV do notimpact upon the gird, but are repelled from it. Electrons from themethane plasma will be drawn to grid 39 and electrode 38. This confinesthe ions to the region above the grid electrode 39. If maximuminteraction between ions and particulates is desired, and grid erosionis tolerable, the opposite polarity of the external d.c. supply voltagesource 43 may be used, so that ions penetrate through the apertures ofgrid electrode 39 and begin to interact very energetically withparticulate surfaces even in the region between electrodes 40 and 39.This may be limited by the supply of new ions generated by the a.c.voltage in the region between electrodes 39 and 38. A limiting case ofthis type of operation includes positive ion neutralization of negativecharges on particulates before they are lifted up off of electrode 40.While possible, this limits the available surface area on the particleswhich is subject to ionic impact. The lower conversion rate thusachieved would be at least partially offset by the additional conversiondue to the much larger ionic impact energy.

Although the a.c. electric field between electrodes 39 and 38 isillustrated as a dipole field, it is possible that a quadrupolar field,or a higher order multipolar field, could be established in the region,by suitable segmentation and reconnection of electrodes 39 and 38, withseparate additional external potential sources connected between pairsof said segments. Ionic paths (neglecting collisions with particles)would be curved, and oscillatory, rather than linear and oscillatory.Such curved paths could be either in the vertical plane, or in thehorizontal plane or both.

Particulate natural minerals, such as metallic oxides, sulfides,chlorides, fluorides, carbonates, sulfates, nitrates, and more complexcompounds can be reduced in this apparatus. This formation of eitherhydrides, organometallics, or pure metal particles of the elements inGroups I-VI of the Periodic Table may be expected, and other compoundsare possible.

Particles composed of high hydrocarbons, such as coal, may be combinedwith methane in this apparatus to yield a rich spectrum of hydrocarbongases and liquids which are more easily transported by pipelines andutilized as fuels and in further chemical processes. Inorganic contentof such feedstock, such as silica or other minerals, can also bedecomposed and reduced. Mixed materials such as oil shale, tar sands,and carbonaceous shales may also be treated. Waste particulates fromcombustion or from industrial processes may also be treated.

Output gases may be separated in low-temperature/low-pressuredistillation stages for selection of components for specific uses. Suchequipment is conventional and is not shown.

Inasmuch as the present invention is subject to many variations,modifications, and changes in detail, it is intended that all subjectmatter discussed above or shown in the accompanying drawing beinterpreted as illustrative and not in a limiting sense. Suchmodifications and variations are included within the scope of thisinvention as defined by the following claims.

What is claimed is:
 1. A method for the conversion of substances initially in particulate form into other substances which may be in gaseous form or in particulate form, in a particulate projection and plasma reaction chamber, comprising the steps of:introducing the particulates .into a first region where they are electrically charged, and projected into a second region; creating and maintaining an energetic plasma in said second region; providing repetitive interactions between said plasma and said particulates; removing resulting gaseous products and particulate products from said chamber.
 2. A method as claimed in claim 1, wherein said plasma is created using a hydrocarbon source gas.
 3. A method as claimed in claim 1, wherein said substances in particulate form are naturally-occurring minerals.
 4. A method as claimed in claim 1, wherein said substances in particulate form are carbonaceous.
 5. A method as claimed in claim 1, wherein said substances in particulate form are waste products from combustion processes or from industrial processes. 